1. Field of the Invention
The present invention relates to an information recording/reproduction apparatus, a head levitation height control method, and a head levitation control circuit that control a head levitation height relative to a recording medium.
2. Description of the Related Art
In a magnetic disk apparatus, a slider incorporating a magnetic head uses the airflow caused by disk rotation to levitate in the very vicinity of the disk surface. As the levitation height is reduced, sensitivity becomes higher as well as unnecessary broadening of a magnetic field can be suppressed. Therefore, the reduction in levitation height of the slider is indispensable for increasing the capacity of a magnetic disk apparatus.
Currently, along with advancement in design improvement of a levitation surface and slider processing technique, a head levitation height is reduced to about 10 nm. However, improvement in terms of design is being pushed to the limit and it is necessary to perform active control of the levitation height for further reduction in the levitation height.
As prior arts relating to the present invention, there are known the following methods: a method that applies a current to a heat element resistor provided in a head portion to deform the head portion due to generated heat to thereby reduce the levitation height (projecting the head) (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publication No. 5-20635 (Patent Document 1)); a method that applies heat to the resistor, like the method of above Patent Document 1, to increase the levitation height (reduce the projecting amount of the head) (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publication No. 2004-241092 (Patent Document 2)); a method that applies a voltage to a piezoelectric element provided on the back surface of the slider to warp the back surface of the slider to thereby increase the levitation height (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publications Nos. 62-250570 and 5-347078 (Patent Documents 3 and 4)); an electrostatic levitation method that utilizes Coulomb's force to change the head levitation height (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publication No. 61-113117 (Patent Document 5)); and a method that deforms a suspension supporting the slider to change the head levitation height (refer to, e.g., Jpn. Pat. Appln. Laid-Open Publication No. 61-172285 (Patent Document 6)).
However, a method such as one disclosed in the above Patent Document 1, 2, or 5 can change the levitation height by at most 5 nm. Further, the method of Patent Document 1 can reduce the levitation height, but cannot increase it. Similarly, the methods of Patent Documents 2, 3, and 4 can increase the levitation height but cannot reduce it.
In a method like Patent Document 1 or 2, in which deformation due to generated heat is utilized, applied current and deformation amount are proportional to each other, so that a power consumption corresponding to the deformation amount is always required in order to maintain a given levitation height. This power consumption is a serious problem for portable-use applications in which power consumption is severely restricted. In a method like Patent Document 1, 2, or 6, it is impossible to change the levitation height at high speed. For example, in the methods of Patent Documents 1 and 2, a time delay from several tens of ms to several hundreds of ms is inevitable in terms of time constant of heat conduction. In the method using the heat deformation, it is impossible to follow the high speed levitation change caused due to waviness of the disk surface.